Plasma processor

ABSTRACT

This invention includes a first filter ( 27 ) connected between a susceptor ( 21 ) and ground and having a variable impedance, a sensor ( 28 ) for detecting an electrical signal based on the state of a plasma (P) generated in a process chamber ( 11 ), and a control means ( 36 ) for controlling the impedance of the first filter ( 27 ) on the basis of a detection result output from the sensor ( 28 ). Thus, a preferable plasma distribution to match the object of the plasma process can be realized.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a plasma processing apparatuswhich performs a predetermined process by generating a plasma.

[0002] In the manufacture of a semiconductor device or flat paneldisplay, plasma processing apparatuses are used often to performprocesses such as formation of an oxide film, crystal growth of asemiconductor layer, etching, and ashing. A case wherein a plasmaprocessing apparatus is applied to an etching apparatus will bedescribed. FIG. 9 is a view showing an arrangement of an etchingapparatus using a conventional plasma processing apparatus.

[0003] A susceptor 521 having a support surface for placing a wafer Wthereon and an upper electrode 531 parallel to the support surface ofthe susceptor 521 are arranged in a process chamber 511. The susceptor521 also serves as a lower electrode.

[0004] Exhaust ports 513 for evacuating the interior of the processchamber 511 to a predetermined vacuum degree are formed in the bottom ofthe process chamber 511, and a gas supply nozzle 514 for supplyingprocess gases into the process chamber 511 is provided to the side wallof the process chamber 511.

[0005] The upper electrode 531 is connected to an RF power supply 534,which outputs an RF power of, e.g., 60 MHz, through a matching circuit535. When the power supply 534 starts supplying the RF power with afrequency of 60 MHz to the upper electrode 531, an electric field with afrequency of 60 MHz is formed in the space between the upper electrode531 and susceptor 521. This electric field ionizes the gases suppliedfrom the gas supply nozzle 514 to generate a plasma P. The plasma P isutilized for etching the wafer W placed on the support surface of thesusceptor 521.

[0006] When performing an etching process, the distribution of theplasma P is preferably not distributed in the entire process chamber 511but distributed over the support surface of the susceptor 521 with ahigh density. This is because with this distribution, the etchingprocess can be performed efficiently and etching of the inner wallsurface of the process chamber 511 by the plasma P can be suppressed, sothat the service life of the process chamber 511 can be prolonged.

[0007] In view of this, according to this etching apparatus, a filter527 formed of an LC series resonance circuit is inserted between thesusceptor 521 and ground. The resonance frequency of the filter 527 isset to 60 MHz, which is the same as the frequency of the RF power to besupplied to the upper electrode 531. For example, if L=0.07 μH and C=100pF, the resonance frequency of the filter 527 can be set to 60 MHz. Thefrequency characteristics of the filter 527 are as indicated by a solidline in FIG. 10, and the impedance is the minimum when the frequency is60 MHz.

[0008] When the plasma P is generated, however, an ion sheath SH isformed between the plasma bulk and the upper electrode 531 or susceptor521. An electric field is formed in the layer of the ion sheath SH, andaccordingly a new capacitance is generated between the upper electrode531 and susceptor 521 by the generation of the plasma P. For example,assume that a capacitance of 200 pF is generated by the ion sheath SH.Even when the resonance frequency of the filter 527 is designed at 60MHz as described above, the frequency characteristics of the first pathextending from the upper electrode 531 to reach ground through thesusceptor 521 and filter 527 are as indicated by a broken line in FIG.10, and the resonance frequency of the first path becomes 74 MHz. Hence,even if the filter 527 is designed without considering the influence ofthe ion sheath SH as in the prior art, the frequency of the RF powercannot cause resonance when the plasma P is generated, so the impedanceof the first path cannot be decreased sufficiently. Consequently, theplasma P cannot be sufficiently concentrated on the support surface ofthe susceptor 521.

[0009] When process conditions such as the power value of the RF powerto be supplied to the upper electrode 531, the pressure in the processchamber 511, the type and mixing ratio of the process gases, and thelike are changed, the capacitance obtained by the ion sheath SHdescribed above also changes. Accordingly, even when the filter 527 isdesigned with a consideration to the influence of the ion sheath SHformed when a plasma is generated under predetermined processconditions, if the process conditions differ from the predeterminedprocess conditions, the frequency (e.g., 60 MHz) of the RF power cannotcause resonance.

[0010] When the etching process is to be performed, the plasma P ispreferably concentratedly distributed on the support surface of thesusceptor 521, as described above. When the interior of the processchamber 511 is to be cleaned, the plasma P is rather preferably diffusedin the entire process chamber 511. In this manner, preferable plasmadistribution differs depending on the object of the process.Conventionally, the filter 527 is designed for the etching process, andaccordingly its characteristics are fixed. Hence, the interior of theprocess chamber 511 cannot be cleaned under preferable conditions.

[0011] When deposits attaching to the inner wall surface or the like ofthe process chamber 511 peel off during the etching process and formparticles, the particles attach to the wafer W to decrease the yield ofelements to be formed on the wafer W. Therefore, desirably no depositpreferably attaches at all to the inner wall surface of the like of theprocess chamber 511, or if any, they desirably attach stably so theywill not peel off during the process. The deposit attaching state,however, changes depending on the process conditions as described above.When the process is performed after changing the process condition, thedeposit attaching state changes to form particles, which may decreasethe yield.

[0012] The above problems arise not only when the plasma processingapparatus is applied to an etching apparatus, but are common amongplasma processing apparatuses.

SUMMARY OF THE INVENTION

[0013] The present invention has been made to solve the above problems,and has as its object to realize a preferable plasma distribution inaccordance with the object of the plasma process.

[0014] In order to achieve the above object, the present invention ischaracterized by comprising a first filter connected between ground anda susceptor which is arranged in a process chamber to place a targetobject thereon, and having variable circuit characteristics, a sensorwhich detects a state of a plasma generated in the process chamber, andcontrol means for controlling the circuit characteristics of the firstfilter on the basis of a detection result output from the sensor. Thus,the impedance of the first path, which extends from electric fieldgenerating means for generating an AC electric field at a positionopposing the support surface of the susceptor to ground through thesusceptor and filter, can be adjusted in accordance with the state ofthe plasma.

[0015] In order to perform a process such as etching or CVD, if theplasma distributed over a region opposing the support surface of thesusceptor is to be maximized, the control means may control the circuitcharacteristics of the first filter in such a direction that theimpedance of the first path decreases (this mode is called the firstcontrol mode). In order to clean the interior of the process chamber, ifthe plasma is to be diffused in the entire process chamber so the plasmareaching the inner wall surface of the process chamber is maximized, thecontrol means may control the circuit characteristics of the firstfilter in such a direction that the impedance of the first pathincreases (this mode is called the second control mode).

[0016] When the state of the plasma is detected in this manner and thecircuit characteristics of the first filter are controlled on the basisof the detection result, even if a plasma is generated to form an ionsheath or even if the state of the ion sheath changes, a plasmadistribution appropriate for a plasma process can be realized withoutbeing adversely affected by the ion sheath or its change.

[0017] In the case of a parallel-plate plasma processing apparatus, theelectric field generating means comprises a counter electrode arrangedto be parallel to the support surface of a susceptor, and a power supplyfor supplying an RF power to the electrode. The sensor suffices as faras it detects, e.g., the value of a current flowing through the firstfilter, the value of a voltage applied to the first filter, the phasedifference between the current and voltage, the value of a currentflowing through the counter electrode, the value of the voltage appliedto the counter electrode, the phase difference between thecurrent/voltage of the first filter and the current/voltage of thecounter electrode, or the like. An output signal from a sensor attachedto the wall (excluding the susceptor and counter electrode) or window ofthe process chamber may be used to control the first filter.Alternatively, output signals from sensors may be used together.

[0018] The control means may have a switch that performs switchingoperation between the first control mode and the second control mode ina multilevel manner or arbitrarily. The two control modes can berealized by the switching operation. Thus, not only a process such asetching but also cleaning can be performed in a preferable state.

[0019] The control means may perform switching operation among aplurality of control modes, thus realizing a predetermined plasmadistribution corresponding to each of the control modes in the processchamber. Hence, even if the process conditions change and the state of adeposit attaching to the inner wall surface of the process chamberchanges, if the amount of plasma reaching the inner wall surface of theprocess chamber is adjusted in accordance with the changed state,deposits can be suppressed from peeling off to form particles.

[0020] The control means may have the function of changing the circuitcharacteristics of the first filter during a process. For example, theamount of plasma reaching the inner wall surface of the process chambermay be changed periodically, or the amount of plasma reaching the innerwall surface may be changed on the basis of the temperature or the likeof the wall of the process chamber. Then, the deposit attaching to theinner wall surface of the process chamber can be stabilized.

[0021] When the sensor is of a type that detects the value of a currentflowing through the first filter, the control means may control thecircuit characteristics of the first filter in such a direction that thevalue of the current increases if the first control mode is selected,and may control the circuit characteristics of the first filter in sucha direction that the value of the current decreases if the secondcontrol mode is selected.

[0022] When the sensor is of a type that detects the value of a voltageapplied to the first filter, the control means may control the circuitcharacteristics of the first filter in such a direction that the valueof the voltage decreases if the first control mode is selected, and maycontrol the circuit characteristics of the first filter in such adirection that the value of the voltage increases if the second controlmode is selected.

[0023] When the sensor is of a type that detects the number of ionsreaching a predetermined region of the inner wall surface of the processchamber, the control means may control the circuit characteristics ofthe first filter in such a direction that the number of ions decreasesif the first control mode is selected, and may control the circuitcharacteristics of the first filter in such a direction that the numberof ions increases if the second control mode is selected.

[0024] The control means may control the circuit characteristics of thefirst filter to match a value obtained by arithmetic process of thedetection result output from a single or a plurality of sensors. Then,more appropriate control can be performed than in a case wherein thedetection result is directly used for control.

[0025] The present invention further may further comprise a power supplyconnected to the susceptor to apply a bias across the susceptor and theelectric field generating means, and a second filter connected betweenthe electric field generating means and ground and having variablecircuit characteristics. The control means may control the circuitcharacteristics of the second filter on the basis of in the detectionresult output from the sensor. When a bias is applied across thesusceptor and electric field generating means, the energy and anisotropyof the plasma can be controlled. At this time, the impedance of thesecond path extending from the susceptor to ground through the electricfield generating means and the second filter can be adjusted inaccordance with the state of the plasma. Even if a plasma is generatedto form an ion sheath or even if the state of the ion sheath changes,correct control can be performed without being adversely affected by theion sheath or its change.

[0026] The sensor suffices as far as it detects, e.g., the value of acurrent flowing through the second filter, the value of a voltageapplied to the second filter, the phase difference between the currentand voltage, the value of a current flowing through the susceptor, thevalue of the voltage applied to the susceptor, the phase differencebetween the current/value of the second filter and the current/voltageof the susceptor, or the like. An output signal from a sensor attachedto the wall (excluding the susceptor and counter electrode) or window ofthe process chamber may be used to control the second filter.Alternatively, output signals from sensors may be used together.

[0027] When the sensor is of a type that detects the value of a currentflowing through the second filter, the control means may control thecircuit characteristics of the second filter in such a direction thatthe value of the current increases.

[0028] When the sensor is of a type that detects the value of a voltageapplied to the second filter, the control means may control the circuitcharacteristics of the second filter in such a direction that the valueof the voltage decreases.

[0029] When the sensor is of a type that detects the number of ionsreaching a predetermined region of the inner wall surface of the processchamber, the control means may control the circuit characteristics ofthe second filter in such a direction that the number of ions decreases.

[0030] The control means may control the circuit characteristics of thefirst and second filters to match a value obtained by arithmetic processof the detection result output from a single or a plurality of sensors.Then, more appropriate control operation can be performed than a casewherein the detection result is directly used for control.

[0031] The control means may appropriately control the circuitcharacteristics of the first filter such that occurrence of abnormaldischarge in the process chamber is suppressed. Alternatively, thecontrol means may appropriately control the circuit characteristics ofthe first and second filters such that occurrence of abnormal dischargein the process chamber is suppressed.

[0032] The first filter may be formed to include an inductance of notless than 5 μH or a capacitance of not more than 1,000 pF or.Alternatively, the first and second filters may be formed to include aninductance of not less than 5 μH or a capacitance of not more than 1,000pF. Then, even when the inductance and capacitance obtained by the ionsheath change in accordance with the process conditions, the impedancesof the first and second paths can be adjusted easily in accordance withthe state of the plasma by only slightly changing the circuitcharacteristics of the filters, or even without changing them at all.

[0033] The first filter may have a first module for blocking a DCcomponent from passing therethrough, and a second module with a variablecircuit constant against a frequency of an AC electric field. When abias power supply is connected to the susceptor, the first filter mayalso have a third module for blocking a frequency component of the biasfrom passing therethrough. In this case, the first filter may have ablocking plate for electrostatically or electromagnetically blocking thefirst and second modules and the third module from each other.

[0034] The second filter may have a first module for blocking a DCcomponent from passing therethrough, a second module with a variablecircuit constant against the frequency of the bias, and a third modulefor blocking the frequency component of the RF electric field frompassing therethrough. In this case, the second filter may have ablocking plate for electrostatically or electromagnetically blocking thefirst and second modules and the third module from each other.

BRIEF DESCRIPTION OF DRAWINGS

[0035]FIG. 1 is a view showing the arrangement of an etching apparatusaccording to the first embodiment of the present invention;

[0036]FIG. 2 is a circuit diagram showing the arrangement of a firstfilter;

[0037]FIG. 3 is a view showing the arrangement of the sensor shown inFIG. 1;

[0038]FIG. 4 is a graph showing the frequency characteristics of a firstpath extending from an upper electrode to reach ground through asusceptor and filter;

[0039]FIG. 5 is a view showing the arrangement of an etching apparatusaccording to the second embodiment of the present invention;

[0040]FIG. 6 is a view showing the arrangement of an etching apparatusaccording to the third embodiment of the present invention;

[0041]FIG. 7 is a circuit diagram showing the arrangement of a secondfilter;

[0042]FIG. 8 is a view showing an arrangement in which the first filterand a matching circuit are integrally formed;

[0043]FIG. 9 is a view showing an arrangement of an etching apparatususing a conventional plasma processing apparatus; and

[0044]FIG. 10 is a graph showing the frequency characteristics of thefilter used in the etching apparatus shown in FIG. 9, and the frequencycharacteristics of a path extending from the upper electrode to reachground through a susceptor and filter.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The embodiments of the present invention will be described indetail with reference to the drawings. A case will be described whereinthe present invention is applied to an etching apparatus.

[0046] First Embodiment

[0047]FIG. 1 is a view showing the arrangement of an etching apparatusaccording to the first embodiment of the present invention. In FIG. 1,part of the arrangement shows its sectional structure.

[0048] A process chamber 11 of this etching apparatus is defined in ahermetically closeable cylindrical process vessel 12. The process vessel12 is made of a conductive material such as aluminum. Exhaust ports 13communicating with a vacuum pump (not shown) are formed in the bottom ofthe process vessel 12, and can set the process chamber 11 to apredetermined vacuum degree.

[0049] A support table 22 is provided to the bottom of the processvessel 12 through an insulating plate 23, and a cylindrical columnarsusceptor 21 is fixed on the support table 22. The susceptor 21 has ahorizontal support surface for placing a wafer (target object) W as anetching target thereon. The susceptor 21 also serves as a lowerelectrode, and is made of a conductive material such as aluminum.

[0050] A circular disk-like upper electrode 31 having a plurality ofthrough holes 31A is arranged in the upper space of the process chamber11 to be parallel to the support surface of the susceptor 21. The upperelectrode 31 is made of a conductive material such as single-crystalsilicon, and is fixed to the lower portion of a support 32.

[0051] The support 32 is made of a conductive material such as aluminum,and forms a hollow circular column in it to have the upper electrode 31as its bottom surface. The support 32 is so attached as to close theupper opening of the process vessel 12 through an insulating ring 33. Agas inlet port 32A is formed at the center of the upper surface of thesupport 32, and is connected to a gas inlet pipe 39. Process gases suchas Ar, O₂, and the like are introduced from the gas inlet pipe 39.

[0052] An RF power supply 34 is connected to the support 32 having thesame potential as that of the upper electrode 31. The RF power supply 34suffices as far as it outputs an RF power with a frequency of aboutseveral ten MHz and a power value of about 5 kW. In this embodiment,note that the RF power supply 34 outputs an RF power with a frequency of60 MHz and a power value of 3.3 kW. A matching circuit 35 is connectedbetween the RF power supply 34 and support 32 to match their impedances.For example, the matching circuit 35 is formed of a variable capacitor,and its capacitance is controlled by a controller 36.

[0053] The susceptor 21 is grounded through a first filter 27 formed ofa resonance circuit having a variable reactance. The path extending fromthe upper electrode 31 to reach ground through the susceptor 21 andfilter 27 will be called the first path. When the reactance of thefilter 27 is changed, the impedance of the first path against thefrequency (60 MHz) of the RF power supplied to the upper electrode 31can be adjusted.

[0054] Furthermore, a sensor 28 for detecting an electrical signalflowing through the filter 27 on the basis of the state of a plasma Pgenerated in the process chamber 11, and a controller for controllingthe reactance of the filter 27 on the basis of a detection result outputfrom the sensor 28 are provided. In the etching apparatus shown in FIG.1, the controller 36 for the matching circuit 35 is provided with thefunction of the control means for the filter 27. Alternatively, acontrol means for the filter 27 may be provided separately.

[0055] The filter 27 will be further described.

[0056]FIG. 2 is a circuit diagram showing the arrangement of the filter27. The filter 27 has a first module 27A for blocking a DC componentfrom passing therethrough, and a second module 27B with a variablereactance against the frequency of the RF power supplied to the upperelectrode 31.

[0057] When the RF power supply 34 supplies the RF power to the upperelectrode 31, a DC voltage of about several hundred V is generated inthe susceptor 21. The first module 27A is formed of, e.g., a capacitor27 p, and blocks a DC component from passing from the susceptor 21 toground, so that short-circuiting of the DC component can be prevented.

[0058] The second module 27B is formed of, e.g., a series circuit (LCseries resonance circuit) of a coil 27 r and capacitor 27 q. In thiscase, it suffices as far as at least one of the inductance of the coil27 r and the capacitance of capacitor 27 q is variable. In thisembodiment, note that the inductance of the coil 27 r is variable, whilethe capacitance of the capacitor 27 q is fixed. When the second module27B is an LC series resonance circuit as shown in FIG. 2, the capacitor27 q of the second module 27B can also serve as the capacitor 27 p ofthe first module 27A.

[0059] The reactance of the filter 27 which is formed of an inductance L(that is, the inductance of the coil 27 r) and capacitance C (that is,synthetic capacitance of the capacitors 27 p and 27 q) is designed byconsidering an inductance LSH and capacitance CSH obtained by an ionsheath SH and the structures of the process vessel 12 and electrodes(susceptor 21 and upper electrode 31), such that under predeterminedprocess conditions a resonance frequency f1 of the first path is equalto the frequency (60 MHz) of the RF power supplied to the upperelectrode 31 and the impedance for this frequency is the minimum. Notethat the range of the reactance of the filter 27 is set such that theimpedance of the first path can be minimized even when the inductanceL_(SH) and capacitance C_(SH) obtained by the ion sheath SH change inaccordance with the process conditions, and such that the impedance ofthe first path can be sufficiently increased when the interior of theprocess chamber 11 is to be cleaned.

[0060] For example, the filter 27 is designed under the followingprocess conditions:

[0061] frequency of RF power: 60 MHz, power value: 1.0 kW to 5.0 kW

[0062] process pressure: 0.6 Pa to 10 Pa

[0063] process gases: Ar=100 sccm to 500 sccm,

[0064] O₂=5 sccm to 15 sccm

[0065] (sccm=standard cubic centimeter per minute)

[0066] The capacitance C_(SH) obtained by the ion sheath SH which isformed when the plasma P is generated under these conditions is about100 pF to 300 pF. The resonance frequency f1 of the first path includingthe filter 27 is expressed as follows:

f1=1/{2π(LC ₁)^(1/2})  (1)

C1=C·C _(SH)/(C+C _(SH)))  (2)

[0067] Note that C=200 pF and 50 nH≦L≦100 nH are set so that f1=60 MHzis obtained for C_(SH)=200 pF.

[0068] Alternatively, the filter 27 may be formed by using a fixedinductance L sufficiently larger than the upper limit of the variablerange of the inductance LSH obtained by the ion sheath SH orsufficiently smaller than the lower limit of the variable range of thecapacitance C_(SH) obtained by the ion sheath SH. In this case, thefixed inductance L is set to 5 μH or more and the fixed capacitance C isset to 1,000 pF or less. Then, the range of the reactance of the filter27 can be set such that even if the inductance L_(SH) and capacitanceC_(SH) of the ion sheath SH change in accordance with the processconditions, the impedance of the first path can be minimized orincreased to be sufficiently large without being adversely affected bythe changes in inductance L_(SH) and capacitance C_(SH).

[0069] Alternatively, the filter 27 may be formed of only the capacitor27 q, and the LC resonance circuit may be formed by utilizing theinductance of an interconnection that connects the susceptor 21 toground through the filter 27.

[0070] The sensor 28 will be further described.

[0071]FIG. 3 is a view showing the arrangement of the sensor 28. Thesensor 28 is formed of an RF current sensor 28A which detects the valueof the current flowing through the filter 27 and outputs it to thecontroller 36, and an RF voltage sensor 28B which detects the value ofthe voltage applied to the filter 27 and outputs it to the controller36.

[0072] When filters (not shown) which pass only 60 MHz are inserted onthe output sides of the current sensor 28A and voltage sensor 28B,respectively, only the frequency of the RF power supplied to the upperelectrode 31 can be detected accurately.

[0073] The controller 36 serving as the control means for the filter 27will be further described.

[0074] When the sensor 28 comprises the current sensor 28A and voltagesensor 28B, the controller 36 has the function of obtaining a phasedifference between the current and voltage detected by the sensor 28 andcalculating the power consumption value of the filter 27, and thefunction of controlling the reactance of the filter 27 on the basis ofthe detected current value or voltage value and the calculated powervalue. Alternatively, an RF equivalent circuit of the process vessel 12may be stored in the controller 36 in advance, so the controller 36 hasthe function of calculating a current flowing through the susceptor 21and the side wall of the process vessel 12 from the output of the filter27, thus controlling the reactance of the filter 27.

[0075] Regarding reactance control of the filter 27, it may be performedalone, or may be performed in combination with capacitance control ofthe matching circuit 35 in accordance with a predetermined sequence.

[0076] The controller 36 has a switch (not shown) that performsswitching operation between the first control mode of controlling suchthat the plasma P distributed over a region opposing the support surfaceof the susceptor 21 becomes maximum, and the second control mode ofcontrolling such that the plasma P reaching the inner wall surface ofthe process chamber 11 becomes maximum. The first control mode isselected when performing an etching process. The second control mode isselected when performing cleaning.

[0077] When the first control mode is selected, the controller 36controls the reactance of the filter 27 such that the impedance of thefirst path against the frequency of the RF power supplied to the upperelectrode 31 becomes minimum. For example, the capacitance C of the efilter 27 is controlled such that the value of the current flowingthrough the filter 27 becomes maximum. When the second control mode isselected, the controller 36 controls the reactance of the filter 27 suchthat the impedance of the first path against the frequency of the RFpower becomes sufficiently large. For example, the capacitance C of thefilter 27 is controlled such that the value of the current flowingthrough the filter 27 becomes sufficiently small.

[0078] In this manner, the controller 36 may perform control on thebasis of the value itself of the current flowing through the filter 27.More preferably, the controller 36 estimates and controls the totalcurrent input to the susceptor 21 by considering the current flowingfrom the susceptor 21 to other members and circuits such as an insulator(not shown).

[0079] The reactance of the filter 27 may be controlled such that thevalue of the voltage applied to the filter 27 becomes large or small.

[0080] As described above, the detection result output from the sensor28 as the detected current value or voltage value may be directly usedfor control. Alternatively, a value obtained by applying the detectionresult to a predetermined model and subjecting it to an arithmeticprocess may be used for control. The model means an expression forcalculating an index indicating the plasma distribution in the processchamber 11 at a given time from, e.g., the value of the current passingthrough the filter 27. When this model is used, more appropriate controlcan be performed.

[0081] The operation of the etching apparatus shown in FIG. 1 will bedescribed.

[0082] The operation during the etching process will be described first.

[0083] First, with the wafer W being placed on the support surface ofthe susceptor 21, the interior of the process chamber 11 is set to avacuum degree of, e.g., about 2.7 Pa. While maintaining this vacuumdegree, Ar and O₂ are introduced from the gas inlet pipe 39 to the spacebetween the support 32 and upper electrode 31 at flow rates of 400 sccm.These gases diffuse in the space and are supplied into the processchamber 11 through the plurality of through holes 31A formed in theupper electrode 31. The gases supplied into the process chamber 11 atthis time are uniformly discharged to the target surface of the wafer W.

[0084] In this state, the RF power supply 34 supplies an RF power with afrequency of 60 MHz and a power value of 3.3 kW to the upper electrode31. The RF power forms an AC field with a frequency of 60 MHz in theprocess chamber 11, and flows to ground from the susceptor 21 or processvessel 12. The electric field formed in the process chamber 11 ionizesthe gases supplied in the process chamber 11 to generate the plasma P.At this time, the ion sheath SH accompanying an electric field is formedaround the plasma P. The ion sheath SH newly generates a capacitance CSHof about 200 pF between the upper electrode 31 and susceptor 21.

[0085] When the plasma P stabilizes, the filter 27 detects the value ofthe current flowing through the filter 27 interposed between thesusceptor 21 and ground and the value of the voltage across the filter27, and outputs them to the controller 36. The controller 36 calculatesthe value of the power from the detected current value and voltagevalue. In the controller 36, the first control mode appropriate for theetching process has been selected. Thus, the controller 36 controls thereactance of the filter 27 in such a direction that the detected currentvalue increases, and decreases the impedance of the first path extendingfrom the upper electrode 31 to ground through the susceptor 21 andfilter 27.

[0086]FIG. 4 is a graph showing the frequency characteristics of thefirst path including the filter 27. The solid line indicates thecharacteristics of the resonance frequency f1 being 60 MHz, and thebroken line indicates the characteristics of the resonance frequency f1being 74 MHz. As is apparent from FIG. 4, the impedance of the firstpath against 60 MHz becomes minimum when the resonance frequency f1 ofthe first path is 60 MHz. Accordingly, the capacitance C of the filter27 is controlled such that the resonance frequency of the first pathbecomes 60 MHz. When the capacitance C of the filter 27 is 200 pF and acapacitance C_(SH) of about 100 pF to 300 pF is generated due to theinfluence of the ion sheath SH, the inductance L of the filter 27 isadjusted within a range of almost 50 nH to 110 nH, as is apparent fromequations (1) and (2).

[0087] Detection with the sensor 28 and control of the filter 27 withthe controller 36 on the basis of this detection result may be performedonce, and after that the two detection results may be fixed.Alternatively, detection and control may be repeated when necessary.

[0088] In this manner, control operation is performed on the basis ofthe current flowing through the filter 27 such that the impedance of thefirst path against 60 MHz becomes minimum. Then, of the RF powersupplied to the upper electrode 31, its proportion directed to theprocess vessel 12 decreases as compared to the prior art, and itsproportion directed to the susceptor 21 further increases. Hence, thedistribution of the plasma P generated by the RF power does not spreadin the entire process chamber 11 but is concentrated to the supportsurface of the susceptor 21. As a result, the etching process of thewafer W utilizing the plasma P can be performed more efficiently than inthe prior art. The amount of plasma P reaching the inner wall surface ofthe process vessel 12 decreases as compared to the prior art. Thus,etching of the inner wall surface of the process vessel 12 by the plasmaP is suppressed, so that the service life of the process vessel 12 canbe prolonged and formation of the particles can be decreased.

[0089] A case wherein etching process is to be performed under differentprocess conditions will be described. For example, the processconditions are changed as follows:

[0090] frequency of RF power: 60 MHz, power value: 1.0 kW to 1.5 kW

[0091] process pressure: 2.7 Pa

[0092] process gases: Ar=300 sccm to 400 sccm,

[0093] O₂=5 sccm to 20 sccm

[0094] Under these conditions, a capacitance C_(SH) of about 300 pF to400 pF is generated by the ion sheath SH. When the inductance L of thefilter 27 is adjusted within the range of about 50 nH to 60 nH by thesame control as that described above, the resonance frequency of thefirst path is set to 60 MHz, so that the impedance of the first pathagainst 60 MHz can be minimized. Even when the process conditions arechanged and accordingly the state of the ion sheath SH changes, a plasmadistribution appropriate for the etching process can be realized withoutpreparing a filter designed to match the process conditions.

[0095] Cleaning of the interior of the process chamber 11 will bedescribed. Operations until generation of the plasma P and calculationof the power consumption value of the filter 27 are the same as in theetching process.

[0096] When cleaning is to be performed, as the second control mode isselected in the controller 36, the controller 36 controls the reactanceof the filter 27 in such a direction that the value of the detectedcurrent decreases, thus increasing the impedance of the first pathextending from the upper electrode 31 to reach ground through thesusceptor 21 and filter 27.

[0097] As is apparent from FIG. 4, the impedance of the first pathagainst 60 MHz increases as the resonance frequency f1 of the first pathchanges from 60 MHz. Accordingly, in this case, the inductance L of thefilter 27 is controlled such that the resonance frequency of the firstpath largely changes from 60 MHz (excitation frequency). The resonanceof the first path may alternatively be set at a higher or lowerfrequency.

[0098] In this manner, control is performed on the basis of the currentflowing through the filter 27 such that the impedance of the first pathagainst 60 MHz increases. Then, of the RF power supplied to the upperelectrode 31, its proportion directed to the susceptor 21 decreases, andits proportion directed to the process vessel 12 increases. Hence, thedistribution of the plasma P generated by the RF power spreads in theentire process chamber 11, and the plasma P reaching the inner wallsurface of the process chamber 11 increases. Thus, the interior of theprocess chamber 11 can be cleaned efficiently.

[0099] In this manner, the controller 36 can be switched between the twocontrol modes by the switch. Thus, not only the etching process but alsocleaning can be performed in a preferable state.

[0100] In the etching apparatus shown in FIG. 1, the voltage sensor 28Bmay detect the value of the voltage applied to only the capacitors 27 pand 27 q or the coil 27 r that form part of the filter 27.

[0101] The sensor 28 may be formed of only the current sensor 28A. Inthis case, the controller 36 controls the reactance of the filter 27 insuch a direction that the value of the current flowing through thefilter 27 increases or decreases. In this case as well, the controller36 preferably estimates and controls the total current input to thesusceptor 21.

[0102] Although the reactance of the filter 27 is variable, it sufficesas far as the circuit characteristics of the filter 27 including aresistance are variable.

[0103] To minimize the impedance of the first path, a resonancefrequency need not be used. It suffices as far as the impedance isminimized as a consequence.

[0104] Second Embodiment

[0105]FIG. 5 is a view showing the arrangement of an etching apparatusaccording to the second embodiment of the present invention. In FIG. 5,the same portions as in FIG. 1 are denoted by the same referencenumerals, and a description thereof will be omitted when appropriate.

[0106] The etching apparatus shown in FIG. 5 has a quadrupole massspectrometer (to be abbreviated as QMS hereinafter) 29 set on the innerwall surface of a process vessel 12 as a sensor for detecting the stateof a plasma P generated in a process chamber 11. The QMS 29 detects thenumber of plasma ions reaching a predetermined region of the inner wallsurface of the process vessel 12.

[0107] The detection result of the QMS 29 is output to a controller 36A.The controller 36A has the same function as that of the controller 36shown in FIG. 1 except that it controls the reactance of a filter 27 onthe basis of the detection result of the QMS 29 set on the inner wallsurface of the process vessel 12.

[0108] When the first control mode appropriate for an etching process ofa wafer W is selected, the controller 36A controls the reactance of thefilter 27 in such a direction that the number of ions detected by theQMS 29, i.e., the number of ions reaching the inner wall surface of theprocess vessel 12, decreases. Then, the plasma P does not diffuse in theentire process chamber 11 but is distributed over a region opposing thesupport surface of a susceptor 21 at a high density. Thus, in the samemanner as with the etching apparatus shown in FIG. 1, the etchingprocess can be performed more efficiently than in the prior art, and theservice life of the process vessel 512 can be prolonged.

[0109] When the second control mode appropriate for cleaning of theinterior of the process chamber 11 is selected, the controller 36Acontrols the reactance of the filter 27 in such a direction that thenumber of ions detected by the QMS 29, i.e., the number of ions reachingthe inner wall surface of the process chamber 11, decreases. Thus, theinterior of the process chamber 11 can be cleaned efficiently.

[0110] In place of the QMS 29, a current sensor for detecting the valueof a current flowing from the process vessel 12 to ground may be used.In this case, the controller may control the reactance of the filter 27in such a direction that the current value detected by the currentsensor decreases in the first mode, and in such a direction that thecurrent value detected by the current sensor increases in the secondmode.

[0111] In the etching apparatus shown in FIG. 1, the filter 27 iscontrolled on the basis of an electrical signal flowing from thesusceptor 21 to ground, and in the etching apparatus shown in FIG. 5,the filter 27 is controlled on the basis of an electrical signal flowingfrom the process vessel 12 to ground. Alternatively, the two controlschemes may be combined, and the filter 27 may be controlled optimallyon the basis of the two electrical signals.

[0112] Third Embodiment

[0113]FIG. 6 is a view showing the arrangement of an etching apparatusaccording to the third embodiment of the present invention. In FIG. 6,the same portions as in FIG. 1 are denoted by the same referencenumerals, and a description thereof will be omitted when appropriate.

[0114] The etching apparatus shown in FIG. 6 is a two-frequency typeetching apparatus having, in addition to an RF power supply 34 whichsupplies an RF power for exciting a plasma P, an RF power supply 24which supplies an RF power for applying a bias across an upper electrode31 and susceptor 21. When the bias is applied across the upper electrode31 and susceptor 21, etching can be performed while controlling theenergy and anisotropy of the plasma P. The RF power supply 24 maysuffice as far as it outputs an RF power with a frequency of about 100kHz to 13 MHz and a power value of about 1.0 kW to 5.0 kW. In thisembodiment, note that the RF power supply 24 outputs an RF power with afrequency of 2 MHz and a power value of 1.5 kW. When cleaning is to beperformed, an output from the RF power supply 24 is stopped, or the RFpower supply 24 outputs a low power of 100 W to 500 W.

[0115] The RF power supply 24 is connected to the susceptor 21 through amatching circuit 25. The matching circuit 25 matches the impedances ofthe RF power supply 24 and susceptor 21, and is formed of, e.g., avariable capacitor. The capacitor of the matching circuit 25 iscontrolled by a controller 26.

[0116] A support 32 having the same potential as that of the upperelectrode 31 is grounded through a second filter 37 formed of aresonance circuit having a variable reactance. The path extending fromthe susceptor 21 to reach ground through the upper electrode 31, support32, and filter 37 will be called the second path. When the reactance ofthe filter 37 is changed, the impedance of the second path against thefrequency (2 MHz) of the RF power supplied to the susceptor 21 can beadjusted.

[0117] Furthermore, a sensor 38 which detects an electrical signalflowing through the filter 37 and a control means for controlling thereactance of the filter 37 on the basis of the detection result outputfrom the sensor 38 are provided. In the etching apparatus shown in FIG.6, the controller 26 for the matching circuit 25 is provided with thefunction of the control means for the filter 37.

[0118] Regarding the sensor 38 and controller 26, they have the samearrangements and the same functions as those of the sensor 28 andcontroller 36, respectively, shown in FIG. 1. Note that the controller26 as the control means for the filter 37 suffices as far as it has thefunction of controlling the reactance of the filter 37 in such adirection that the impedance of the second path against the frequency ofthe RF power supplied to the susceptor 21 decreases.

[0119] The filter 37 will be further described.

[0120]FIG. 7 is a circuit diagram showing the arrangement of the filter37. The filter 37 has a first module 37A for blocking a DC componentfrom passing therethrough, a second module 37B with a variable reactanceagainst the frequency of the RF power supplied to the susceptor 21, anda third module 37C for blocking the frequency (60 MHz) of the RF powersupplied to the upper electrode 31 from passing therethrough.

[0121] When the RF power supply 24 supplies an RF power to the susceptor21, a DC voltage of about several hundred V is generated in the upperelectrode 31. The first module 37A is formed of, e.g., a capacitor 37 p,and blocks the DC component from passing from the upper electrode 31 toground, thus preventing short-circuiting of the DC component.

[0122] The second module 37B is formed of, e.g., a series circuit (LCseries resonance circuit) of a coil 37 r and capacitor 37 q. In thiscase, it suffices as far as at least one of the inductance of the coil37 r and the capacitance of the capacitor 37 q is variable. In thisembodiment, the inductance of the coil 37 r is variable, while thecapacitance of the capacitor 37 q is fixed. When the second module 37Bis an LC series resonance circuit as shown in FIG. 7, the capacitor 37 qof the second module 37B may also serve as the capacitor 37 p of thefirst module 37A.

[0123] The third module 37C is formed of, e.g., a parallel circuit of acoil 37 t and capacitor 37 s, and is designed to have a high impedanceagainst a frequency in the vicinity of the frequency (60 MHz) of the RFpower to be supplied to the upper electrode 31. Thus, the RF powersupplied to the upper electrode 31 can be prevented from flowing to thefilter 37.

[0124] A blocking plate 37D made of aluminum or ion, which performselectrostatic blocking or electromagnetic blocking, is arranged betweenthe first and second modules 37A and 37B and the third module 37C. Whenelectrical interference occurs between the third module 37C and thefirst and second modules 37A and 37B, the band-blocking ability of thethird module 37C decreases largely, and power loss due to the filter 37occurs. Then, not only the power efficiency decreases, but depending onthe case, an excessive current may also flow through the filter 37 toburn it. When the blocking plate 37D is provided, these problems can beprevented.

[0125] The reactance of the filter 37 having the above arrangement isdesigned such that under predetermined process conditions, a resonancefrequency f2 of the second path becomes equal to the frequency (2 MHz)of the RF power supplied to the susceptor 21 and the impedance againstthis frequency becomes minimum. The range of the reactance is set suchthat even when an inductance LSH and capacitance CSH obtained by an ionsheath SH change in accordance with the process conditions, theimpedance of the second path can be minimized. This is the same as inthe filter 27 shown in FIG. 1.

[0126] For example, to obtain f2=2 MHz under the following processconditions, C=1,500 pF and 1 μH≦L≦50 μH are given.

[0127] RF power supplied to the upper electrode 31

[0128] frequency: 60 MHz, power value: 1.0 kW to 5.0 kW

[0129] RF power supplied to the susceptor 21

[0130] frequency: 2 MHz, power value: 1.0 kW to 5.0 kW

[0131] process pressure: 0.6 Pa to 10 Pa

[0132] process gases: Ar=200 sccm to 400 sccm,

[0133] O₂=5 scam to 20 scam

[0134] Alternatively, the filter 37 may be formed by using a fixedinductance L (e.g., 5 μH or more) sufficiently larger than the upperlimit of the variable range of the inductance L_(SH) obtained by the ionsheath SH, or a fixed capacitance C (e.g., 200 pF or less) sufficientlysmaller than the lower limit of the variable range of the capacitanceC_(SH) obtained by the ion sheath SH.

[0135] In a filter 127, a third module (not shown) for blocking afrequency of 2 MHz is series-connected to the first and second modules27A and 27B shown in FIG. 2, so the 2-MHz RF power supplied from the RFpower supply 24 to the susceptor 21 does not flow to the filter 127which is also connected to the susceptor 21. In this case, the reactanceof the filter 127 is designed such that a resonance frequency f1 of theentire first path including the third module becomes equal to thefrequency (60 MHz) of the RF power supplied to the upper electrode 31.When a blocking plate of aluminum or iron which performs electrostaticblocking or electromagnetic blocking is arranged between the first andsecond modules 27A and 27B and the third module, a decrease in powerefficiency and burning can be prevented.

[0136] Alternatively, a matching circuit 125 including a filter 127 maybe used, as shown in FIG. 8.

[0137] The etching apparatus has the arrangement described above, andcontrol operation is performed on the basis of a current flowing throughthe filter 37 in such a direction that the impedance of the entiresecond path against 2 MHz decreases. Then, of the RF power supplied tothe susceptor 21, its proportion directed to the process vessel 12decreases, while its proportion directed to the upper electrode 31increases. Hence, the energy and anisotropy of the plasma P occurringupon application of a bias can be controlled more accurately than in theprior art. Even when the process conditions change and accordingly thestate of the ion sheath SH changes, the energy and anisotropy of theplasma P can be controlled with the same accuracy.

[0138] The bias applied across the upper electrode 31 and susceptor 21may be either a DC bias or pulsed bias. Hence, a DC power supply may beused in place of the RF power supply 24. As the sensor for detecting thestate of the plasma P, a sensor set to the inner wall surface of theprocess vessel 12, like the QMS shown in FIG. 5, may be used.

[0139] Fourth Embodiment

[0140] The controller 36 shown in FIG. 1 may have a plurality of controlmodes that realize different plasma distributions in the process chamber11, and a switch (not shown) for performing switching operation amongthese control modes.

[0141] For example, in a process that produces a large amount ofdeposits to attach to the inner wall surface of the process vessel 12, acontrol mode with which the amount of plasma P reaching the inner wallsurface of the process vessel 12 increases is selected, and thereactance of the filter 27 is controlled. Then, deposits do not easilyattach to the inner wall surface.

[0142] In a process that produces a small amount of deposits to attachto the inner wall surface of the process vessel 12, a control mode withwhich the amount of plasma P reaching the inner wall surface of theprocess vessel 12 becomes smaller than that described above is selected,and the reactance of the filter 27 is controlled. In this case, theamount of plasma P reaching the inner wall surface may be comparativelyincreased to such a degree that no deposit attaches to the inner wallsurface at all, or may be comparatively decreased to such a degree thatdeposits stably attach to the inner wall surface.

[0143] Therefore, when the process conditions are changed, the controlmode is switched in accordance with the characteristics of the process,and the amount of deposits to attach to the inner wall surface of theprocess vessel 12 is adjusted, so particles formed from peeled-offdeposits can be decreased. Then, the yield of elements to be formed onthe wafer W can be increased.

[0144] The controller 36 shown in FIG. 1 may have the function ofchanging the reactance of the filter 27 during the etching process.

[0145] For example, control operation may be performed by periodicallychanging the amount of plasma P to reach the inner wall surface of theprocess vessel 12 during the process, so the deposits attaching to theinner wall surface of the process vessel 12 stabilize.

[0146] The deposits that are to attach to the inner wall surface of theprocess vessel 12 do not attach easily if the temperature of the innerwall surface increases. In view of this, the temperature of the innerwall surface of the process vessel 12 may be measured, and the amount ofplasma P to reach the inner wall surface may be changed during theprocess on the basis of the measured temperature, so that the depositsattach stably. Alternatively, the lapse time since the start ofgeneration of the plasma P may be measured, and the same controloperation may be performed on the basis of the measured time.

[0147] When the deposits attaching to the inner wall surface of theprocess vessel 12 are stabilized in the above manner, the deposits canbe prevented from peeling off to form particles. This can improve theyield of the elements to be formed on the wafer W.

[0148] When the reactance of the filter 27 is changed during the etchingprocess, the amount or nature of radicals to attach to the inner wallsurface of the process vessel 12 can be changed. If the amount or natureof the radicals to attach to the inner wall surface changes, componentsor amount dissociating from the inner wall surface changes. If optimalradicals are selected, the process performance can be improved.

[0149] At the etching end point, the constitution of the radicals in theprocess chamber 11 changes, and the attaching easiness of the radicalsto the inner wall surface or dissociating easiness of the radicals fromthe inner wall surface changes. Hence, as one of the process conditions,the reactance of the filter 27 may be changed, so the constitution ofthe radicals does not change at the etching end point.

[0150] The reactance of the filter 27 may be controlled by thecontroller 36 in accordance with a preset procedure, or on the basis ofa detection signal such as an EPD (End Point Detection) signalindicating the etching end point.

[0151] The above function of the controller 36 may be provided to thecontroller 26 shown in FIG. 6 as a function for the filter 37.

[0152] Fifth Embodiment

[0153] The controller 36 shown in FIG. 1 may have the function ofappropriately controlling the reactance of the filter 27 so thatoccurrence of abnormal discharge in the process chamber 11 issuppressed.

[0154] For example, the larger the value of the current flowing throughthe filter 27, the more unlikely abnormal discharge occurs. When thevalue of the current flowing through the filter 27 is detected by thecurrent sensor 28A and the reactance of the filter 27 is controlled bythe controller 36 in such a direction that the detected current valueincreases, thus maximizing the current value, then occurrence ofabnormal discharge can be suppressed.

[0155] The reactance of the filter 27 may be controlled on the basis ofthe value of the voltage applied to the filter 27, in place of the valueof the current flowing through the filter 27.

[0156] Whether the maximum value of the current flowing to the filter 27and the like are adjusted to adjustment values that are effective forsuppressing abnormal discharge can be checked from the detection resultof the sensor 28.

[0157] This function of the controller 36 may be provided to thecontroller 26 shown in FIG. 6 as a function for the filter 37.

[0158] As has been described above, according to the above embodiments,a sensor for detecting the state of the plasma, and a control means forcontrolling the circuit characteristics of the first filter connectedbetween the susceptor and ground in accordance with the detection resultare provided. Thus, the impedance of the first path, which extends froman electric field generating means for generating an AC field at aposition opposing the support surface of the susceptor to reach groundthrough the susceptor and filter, can be adjusted in accordance with thestate of the plasma. A preferable plasma distribution in accordance withthe object of the plasma process can be realized, so the processefficiency can be improved. Etching of the inner wall surface of theprocess chamber with the plasma can be suppressed, so the service lifeof the process chamber is prolonged, and occurrence of particles can bedecreased.

[0159] While the above description exemplifies a parallel-plate etchingapparatus, the present invention can also be applied to aninduction-coupled plasma etching apparatus, microwave plasma etchingapparatus, and the like. Naturally, the present invention can be appliednot only to an etching apparatus but also to other plasma processingapparatuses such as a plasma CVD apparatus.

1. A plasma processing apparatus comprising a susceptor arranged in ahermetic process chamber and having a support surface for placing atarget object thereon, and electric field generating means forgenerating an AC field at a position opposing the support surface ofsaid susceptor, thus exciting a plasma, characterized by comprising afirst filter connected between said susceptor and ground and havingvariable circuit characteristics, a sensor which detects a state of theplasma, and control means for controlling the circuit characteristics ofsaid first filter on the basis of a detection result output from saidsensor.
 2. A plasma processing apparatus according to claim 1,characterized in that said control means has a switch that performsswitching operation between a first control mode of maximizing theplasma distributed in a region opposing the support surface of saidsusceptor and a second control mode of maximizing the plasma reaching aninner wall surface of said process chamber, in a multilevel manner orarbitrarily.
 3. A plasma processing apparatus according to claim 1,characterized in that said control means performs switching operationamong a plurality of control modes, thus realizing a predeterminedplasma distribution corresponding to each of the control modes in saidprocess chamber.
 4. A plasma processing apparatus according to claim 3,characterized in that said control means changes the circuitcharacteristics of said first filter during a process.
 5. A plasmaprocessing apparatus according to claim 2, characterized in that saidsensor detects a value of a current flowing through said first filter,and said control means controls in such a direction that the value ofthe current increases if the first control mode is selected, andcontrols in such a direction that the value of the current decreases ifthe second control mode is selected.
 6. A plasma processing apparatusaccording to claim 2, characterized in that said sensor detects a valueof a voltage applied to said first filter, and said control meanscontrols in such a direction that the value of the voltage decreases ifthe first control mode is selected, and controls in such a directionthat the value of the voltage increases if the second control mode isselected.
 7. A plasma processing apparatus according to claim 2,characterized in that said sensor detects a number of ions reaching apredetermined region of the inner wall surface of said process chamber,and said control means controls in such a direction that the number ofions decreases if the first control mode is selected, and controls insuch a direction that the number of ions increases if the second controlmode is selected.
 8. A plasma processing apparatus according to claim 1,characterized in that said control means controls the circuitcharacteristics of said first filter to match a value obtained byarithmetic process of the detection result output from said sensor. 9.An apparatus according to claim 1, characterized in that the apparatusfurther comprises a power supply connected to said susceptor to apply abias between said susceptor and said electric field generating means,and a second filter connected between said electric field generatingmeans and ground and having variable circuit characteristics, and saidcontrol means controls the circuit characteristics of said second filteron the basis of the detection result output from said sensor.
 10. Aplasma processing apparatus according to claim 9, characterized in thatsaid sensor detects a value of a current flowing through said secondfilter, and said control means controls in such a direction that thevalue of the current increases.
 11. A plasma processing apparatusaccording to claim 9, characterized in that said sensor detects a valueof a voltage applied to said second filter, and said control meanscontrols such that the value of the voltage decreases.
 12. A plasmaprocessing apparatus according to claim 9, characterized in that saidsensor detects a number of ions reaching a predetermined region of aninner wall surface of said process chamber, and said control meanscontrols in such a direction that the number of ions decreases.
 13. Aplasma processing apparatus according to claim 9, characterized in thatsaid control means controls the circuit characteristics of said firstand second filters to match a value obtained by arithmetic process ofthe detection result output from said sensor.
 14. A plasma processingapparatus according to claim 1, characterized in that said control meansappropriately controls the circuit characteristics of said first filtersuch that occurrence of abnormal discharge in said process chamber issuppressed.
 15. A plasma processing apparatus according to claim 9,characterized in that said control means appropriately controls thecircuit characteristics of said first and second filters such thatoccurrence of abnormal discharge in said process chamber is suppressed.16. A plasma processing apparatus according to claim 1, characterized inthat said first filter has a capacitance of not more than 1,000 pF or aninductance of not less than 5 μH.
 17. A plasma processing apparatusaccording to claim 9, characterized in that said first and secondfilters have a capacitance of not more than 1,000 pF or an inductance ofnot less than 5 μH.
 18. A plasma processing apparatus according to claim1, characterized in that said first filter has a first module forblocking a DC component from passing therethrough, and a second modulewith a variable circuit constant against a frequency of the AC electricfield.
 19. A plasma processing apparatus according to claim 9,characterized in that said filter has a first module for blocking a DCcomponent from passing therethrough, a second module with a variablecircuit constant against a frequency of AC electric field, and a thirdmodule for blocking a frequency component of the bias from passingtherethrough.
 20. A plasma processing apparatus according to claim 9,characterized in that said second filter has a first module for blockinga DC component from passing therethrough, a second module with avariable circuit constant against a frequency of the bias, and a thirdmodule for blocking a frequency component of the RF electric field frompassing therethrough.
 21. A plasma processing apparatus according toclaim 19, characterized in that said first filter has a blocking platefor electrostatically or electromagnetically blocking said first andsecond modules and said third module from each other.
 22. A plasmaprocessing apparatus according to claim 20, characterized in that saidsecond filter has a blocking plate for electrostatically orelectromagnetically blocking said first and second modules and saidthird module from each other.